DENVER — A temporary treatment plant has begun cleaning up polluted water flowing from the Gold King Mine in Colorado after an accident sent millions of gallons of waste into rivers in three states, the Environmental Protection Agency said Monday. The plant is running 24 hours a day and processing up to 800 gallons per minute, including waste discharging from the mine and water stored in ponds, the agency said. An EPA-led cleanup crew inadvertently released a surge of about 3 million gallons of water tainted with heavy metals from the inactive mine on Aug.